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<kristianpaul>
o/
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<key2>
I'm thinking about making something between a logic analyzer and an oscilloscope using http://www.ti.com/lit/ds/symlink/lm97600.pdf and record the stream on 16 SSD sata disk
<key2>
basically to sniff high speed signal for debugging PHY's for example
<key2>
any thought ?
<cr1901_modern>
SIXTEEN SSDs?
<key2>
yeah
<key2>
its 40Gb/s of data :)
<whitequark>
key2: not gonna work
<key2>
so i thought using 16 mSATA disk on a xc7a200
<key2>
whitequark: ?
<whitequark>
modern SSDs are SLC-buffered MLC
<whitequark>
write performance goes to hell very quickly
<whitequark>
now streaming to 16 HDDs, now we're tlaking
<key2>
HDD take much more room
<whitequark>
they also work
<whitequark>
unlike SSDs
<whitequark>
in this application
<key2>
whitequark: those msata ssd announce sequencial write of 320 to 520 MB/s, it's bs ?
<key2>
another option is MVNe, but I believe the flash inside is more or less the same at the end?
<whitequark>
yes
<key2>
any thechnology of SSD would work ?
<key2>
or only HDD would do it
<whitequark>
SLC SSD would work
<whitequark>
very expensive
<whitequark>
look for "industrial" "heavy duty" "high reliability" SSDs
<whitequark>
they're also much smaller for obvious reasons
<whitequark>
actually you could just buy a bunch of SLC NAND flash and stream directly there
<whitequark>
why bother with SATA?
<key2>
because sata is just 4 pins :)
<whitequark>
and what happens when one of your SATA flashes is slower because it wants to reallocate some sectors?
<whitequark>
with NAND you will never have such an issue
<whitequark>
you do not have guaranteed latency response on SATA SSDs
<key2>
yeah but if all disk are the same, and we write equal amount of raw data on all of them at the same time, why would one disk do something while other are not ?
<whitequark>
because all the NAND flashes on them are different
<whitequark>
some have more bad blocks on them than others
<whitequark>
so, disks are not all the same
<whitequark>
they also degrade differently
<whitequark>
with 2 maybe it would be ok, with 16 you will observe this immediately
<whitequark>
NAND flash gateware is like 100 lines... also you can share the data buses to some extent
<whitequark>
need to check whats the max capacitance there
<key2>
yeah but you run out of IOs
<whitequark>
so, you need 8/16+3+2*n lines per flash bank
<whitequark>
let's say that SSD has four NAND flashes
<whitequark>
assume you can stick 16 of them on a single bank
<whitequark>
you need 204 lines
<whitequark>
if you can only put 8 of them (this is definitely possible) then you need 408 lines
<whitequark>
ah sorry no
<whitequark>
280
<whitequark>
so even less
<whitequark>
thats at 16 bit wide
<key2>
8/16+3+2*n ?
<key2>
u mean 8 + WE+RE+BLE..
<key2>
things like this ?
<whitequark>
i mean IO+CE+CLE+ALE+(RE+WE)*n
<whitequark>
per bank
<whitequark>
where n is count of flashes in a single bank